The invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to toner compositions containing optional charge enhancing additives, which impart or assist in imparting a positive or negative charge to the toner resin particles and can enable toners with rapid admix characteristics; and surface additives. In one embodiment, there are provided in accordance with the present invention toner compositions comprised of resin particles, pigment particles, a charge additive or charge additives such as quaternary ammonium hydrogen bisulfates, including distearyl methyl hydrogen ammonium bisulfate, orthohalophenylbenzoic acids, aluminum complexes, reference U.S. Pat. No. 4,845,003, and copending patent application U.S. Ser. No. 755,919, the disclosure of which is totally incorporated herein by reference, and as surface additives metal oxides coated with a surfactant to provide, for example, toners with improved flow characteristics and of triboelectrical properties substantially independent of the relative humidity of the environment. In one embodiment, the present invention is directed to toners with surface additives comprised of metal oxides, such as hydrophobic oxides, like tin oxide, with a continuous coating of a surfactant, such as TRITON X-114.RTM. which is an octylphenoxy polyethoxy ethanol surfactant, or an AOT.RTM. surfactant which is dioctyl sulfosuccinate, sodium salt, available from Aldrich Chemical Company, and wherein the surface additives are particles in a uniform size with a diameter of, for example, from between about 3 to about 100 nanometers and preferably from about 3 to about 50 nanometers as determined by transmission electron microscopy. Also, the aforementioned toner compositions usually contain pigment particles comprised of, for example, carbon black, magnetites, or mixtures thereof, cyan, magenta, yellow, blue, green, red, or brown components, or mixtures thereof thereby providing for the development and generation of black and/or colored images. The toner compositions of the present invention in embodiments thereof possess excellent admix characteristics as indicated herein, and maintain their triboelectric charging characteristics for an extended number of imaging cycles exceeding, for example, 500,000 in a number of embodiments. The toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic imaging and printing processes, including color processes, such as trilevel and full color process xerography, reference for example copending patent application U.S. Ser. No. 705,995, the disclosure of which is totally incorporated herein by reference.
Toner compositions with surface additives, such as silica like AEROSIL R972.RTM., are known. These additives, which may have a small particle size diameter of 7 to 100 nanometers, may adversely effect the sign, magnitude, and stability of the toner triboelectric charging and wherein the developer charge becomes highly dependent on the relative humidity, disadvantages avoided, or minimized with the invention of the present application. Other disadvantages associated with the prior art surface additives include the high specific gravity of the additives which ranges from about 2.2 grams/cm.sup.3 for silica flow additives to about 4 grams/cm.sup.3 for titania additives. The additives of the present invention can achieve specific gravities approaching about 1.2 grams/cm.sup.3. Reducing the specific gravity of a flow aid, for example, from about 6.95 grams per cm.sup.3 for tin oxide produced by the flame hydrolysis process to about 3.2 grams per cm.sup.3 for tin oxide selected for the toners of the present invention results in a decrease from about 2.0 to about 0.8 in the weight percent of flow aid needed to achieve superior flow of a toner, since the effectiveness of a flow aid depends on its surface area and not on its mass. Therefore, less flow aid is required, resulting in a lowering of the cost of the toner proportional to the lowering of the mass of the flow aid used in a toner composition. Moreover, a lowering of the amount of flow aids will reduce undesired contamination of other components of a xerographic imaging apparatus, such as the Xerox Corporation 5090.RTM., especially the photoconductive imaging member and the fuser components.
The use of small fumed silica particles of diameter ranging from about 7 to about 100 nanometers for the improvement of toner flow properties is known. These materials such as, for example, AEROSIL 380.RTM. available from Degussa, as well as other inorganic oxides, such as for example titania, available from Degussa as DEGUSSA P25.RTM. or alumina, available from Degussa as DEGUSSA ALUMINUM OXIDE C.RTM., are invariably produced by a flame hydrolysis process. One disadvantage of the use of such materials is that they are hydrophilic and thus are sensitive to environment humidity, resulting in a decrease in flow and in triboelectric charge of the toner with increasing humidity. For example, a 50 percent decrease in flow and a 50 percent decrease in charge take place as the humidity of the environment reaches 80 percent RH. A well-known process to reduce the humidity sensitivity of these materials is the surface treatment of the inorganic oxides with a functional silane, such as for example hexadimethylsilane, dimethyldichlorosilane, methyltrichlorosilane, and trimethylchlorosilane. Other surface treatments and/or combinations of different inorganic oxides have also been shown in the prior art. For example, Japanese Publication (JP) 61 250,658 discloses mixtures of negatively and positively charging silicas for toner flow improvement, while Japanese Publication 61 249,059 discloses the use of mixtures of hydrophilic and hydrophobic silicas for improved toner flow.
Similarly, Japanese Publication 62 227,140 discloses the use of negative toners coated in a first step with a positive charge additive, such as, for example, alumina treated with an amine-modified silicone oil and in a second step with a negative charge additive, such as, for example, a silica treated with dimethyldichlorosilane, for improved flow. Another surface treatment for silica has been disclosed in U.S. Pat. No. 4,680,245 which illustrates an aminosilane-treated silica for positive charging of toners. The Japanese patent Japanese Publication 62 172,372 discloses the use of a hydrophilic titania treated with a zirconium aluminum coupling agent to obtain negatively charged toners.
The aforementioned surface treatments of inorganic oxides using hydrolyzable silanes or other coupling agents and the application of this treatment for the modification of the surface properties of inorganic oxides produced by the flame hydrolysis process possess a number of disadvantages when selected for toners. One of the disadvantages associated with the use of such surface-treated inorganic oxides is that their use often results in changes in the charging properties of the toner, resulting in an undesirable lowering by, for example, 30 microcoulombs per gram or raising by, for example, 20 microcoulombs per gram of the toner charge. Moreover, the use of these surface-treated additives also results often in a decrease by, for example, 30 percent of the stability of the toner charge particularly under high humidity conditions, for example 85 percent. These and other disadvantages are avoided with the toners of the present invention.
P. Espiard et al., "A Novel Technique for Preparing Organophilic Silica by Water-In-Oil Microemulsions," Polymer Bulletin, vol. 24, pages 170 to 173 (Spring 1990), the disclosure of which is totally incorporated herein by reference, discloses a technique for preparing ultramicro spherical silica particles containing vinyl groups on their surfaces by a combination of the sol-gel technique and the water-in-oil emulsion technique in which hydrolysis and condensation of tetraethyl siloxane and trimethoxysilylpropyl methacrylate take place. Spherical silica particles with a size range from 20 to 70 nanometers were obtained and the surface concentrations of the double bonds per square nanometer were from 4 to 7.
H. Yamauchi et al., "Surface Characterization of Ultramicro Spherical Particles of Silica Prepared by W/O Microemulsion Method", Colloids and Surfaces, vol. 37, pages 71 to 80 (1989), the disclosure of which is totally incorporated herein by reference, discloses the preparation of ultramicro spherical particles of colloidal silica by the hydrolysis of tetraethoxysilane in the water pool of a water-in-oil (isooctane) microemulsion using Aerosol-OT. The average diameter of the silica spheres obtained was of the order of 10 nanometers and their surface areas were about 100 to 300 square meters per gram. The nitrogen adsorption isotherms of this material indicate that the particles have micropores in contrast to colloidal nonporous silica particles such as AEROSILS.RTM. and those in silica sols having a similar size of particle.
J.C. Giuntini et al., "Sol-gel preparation and transport properties of a tin oxide", Journal of Materals Science Letters, vol. 9, pages 1383 to 1388 (1990), the disclosure of which is totally incorporated herein by reference, disclosed a technique for preparing tin alkoxide by hydrolysis of tin butylate to a tin oxide gel.
Also, developer compositions with charge enhancing additives, which impart a positive charge to the toner resin, are well known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions. In this patent, there are disclosed quaternary ammonium compounds with four R substituents on the nitrogen atom, which substituents represent an aliphatic hydrocarbon group having 7 or less, and preferably about 3 to about 7 carbon atoms, including straight and branch chain aliphatic hydrocarbon atoms, and wherein X represents an anionic function including, according to this patent, a variety of conventional anionic moieties such as halides, phosphates, acetates, nitrates, benzoates, methylsulfates, perchloride, tetrafluoroborate, benzene sulfonate, and the like; U.S. Pat. No. 4,221,856 which discloses electrophotographic toners containing resin compatible quaternary ammonium compounds in which at least two R radicals are hydrocarbons having from 8 to about 22 carbon atoms, each other R is a hydrogen or hydrocarbon radical with from 1 to about 8 carbon atoms, and A is an anion, for example, sulfate, sulfonate, nitrate, borate, chlorate, and the halogens such as iodide, chloride and bromide, reference the Abstract of the Disclosure and column 3; a similar teaching is presented in U.S. Pat. No. 4,312,933 which is a divisional of U.S. Pat. No. 4,291,111; and similar teachings are presented in U.S. Pat. No. 4,291,112 wherein A is an anion including, for example, sulfate, sulfonate, nitrate, borate, chlorate, and the halogens. There are also described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of electrostatic latent images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica.
Also, there is disclosed in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, developer compositions containing as charge enhancing additives organic sulfate and sulfonates, which additives can impart a positive charge to the toner composition. Further, there are disclosed in U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions with resin particles and pigment particles, and as charge enhancing additives alkyl pyridinium compounds. Additionally, other documents disclosing positively charged toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014 4,394,430, and 4,560,635 which illustrates a toner with a distearyl dimethyl ammonium methyl sulfate charge additive.
Moreover, toner compositions with negative charge enhancing additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064, the disclosures of which are totally incorporated herein by reference. The '974 patent discloses negatively charged toner compositions comprised of resin particles, pigment particles, and as a charge enhancing additive ortho-halo phenyl carboxylic acids. Similarly, there are disclosed in the '064 patent toner compositions with chromium, cobalt, and nickel complexes of salicylic acid as negative charge enhancing additives.
Illustrated in U.S. Pat. No. 4,937,157, the disclosure of which is totally incorporated herein by reference, are toner compositions comprised of resin, pigment, or dye, and tetraalkyl, wherein alkyl, for example, contains from 1 to about 30 carbon atoms, ammonium bisulfate charge enhancing additives such as distearyl dimethyl ammonium bisulfate, tetramethyl ammonium bisulfate, tetraethyl ammonium bisulfate, tetrabutyl ammonium bisulfate, and preferably dimethyl dialkyl ammonium bisulfate compounds where the dialkyl radicals contain from about 10 to about 30 carbon atoms, and more preferably dialkyl radicals with from about 14 to about 22 carbon atoms, and the like. The aforementioned charge additives can be incorporated into the toner or may be present on the toner surface. Advantages of rapid admix, appropriate triboelectric characteristics, and the like are achieved with many of the toners of the aforementioned copending application.